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Message-ID: <CAMz4kuLQsrBWjta1s=ZRPgxUd0_+_f-GbJV138tccuMLg2XCLA@mail.gmail.com>
Date: Fri, 9 Aug 2019 18:06:21 +0800
From: Baolin Wang <baolin.wang@...aro.org>
To: Uwe Kleine-König
<u.kleine-koenig@...gutronix.de>
Cc: Thierry Reding <thierry.reding@...il.com>,
Rob Herring <robh+dt@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Orson Zhai <orsonzhai@...il.com>,
Chunyan Zhang <zhang.lyra@...il.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
linux-pwm@...r.kernel.org, DTML <devicetree@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>, kernel@...gutronix.de
Subject: Re: [PATCH 2/2] pwm: sprd: Add Spreadtrum PWM support
Hi Uwe,
On Fri, 9 Aug 2019 at 17:10, Uwe Kleine-König
<u.kleine-koenig@...gutronix.de> wrote:
>
> On Thu, Aug 08, 2019 at 04:59:39PM +0800, Baolin Wang wrote:
> > From: Neo Hou <neo.hou@...soc.com>
> >
> > This patch adds the Spreadtrum PWM support, which provides maximum 4
> > channels.
> >
> > Signed-off-by: Neo Hou <neo.hou@...soc.com>
> > Co-developed-by: Baolin Wang <baolin.wang@...aro.org>
> > Signed-off-by: Baolin Wang <baolin.wang@...aro.org>
> > ---
> > drivers/pwm/Kconfig | 10 ++
> > drivers/pwm/Makefile | 1 +
> > drivers/pwm/pwm-sprd.c | 311 ++++++++++++++++++++++++++++++++++++++++++++++++
> > 3 files changed, 322 insertions(+)
> > create mode 100644 drivers/pwm/pwm-sprd.c
> >
> > diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
> > index a7e5751..4963b4d 100644
> > --- a/drivers/pwm/Kconfig
> > +++ b/drivers/pwm/Kconfig
> > @@ -423,6 +423,16 @@ config PWM_SPEAR
> > To compile this driver as a module, choose M here: the module
> > will be called pwm-spear.
> >
> > +config PWM_SPRD
> > + tristate "Spreadtrum PWM support"
> > + depends on ARCH_SPRD || COMPILE_TEST
>
> I think you need
>
> depends on HAS_IOMEM
OK.
>
> > + help
> > + Generic PWM framework driver for the PWM controller on
> > + Spreadtrum SoCs.
> > +
> > + To compile this driver as a module, choose M here: the module
> > + will be called pwm-sprd.
> > +
> > config PWM_STI
> > tristate "STiH4xx PWM support"
> > depends on ARCH_STI
> > diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
> > index 76b555b..26326ad 100644
> > --- a/drivers/pwm/Makefile
> > +++ b/drivers/pwm/Makefile
> > @@ -41,6 +41,7 @@ obj-$(CONFIG_PWM_ROCKCHIP) += pwm-rockchip.o
> > obj-$(CONFIG_PWM_SAMSUNG) += pwm-samsung.o
> > obj-$(CONFIG_PWM_SIFIVE) += pwm-sifive.o
> > obj-$(CONFIG_PWM_SPEAR) += pwm-spear.o
> > +obj-$(CONFIG_PWM_SPRD) += pwm-sprd.o
> > obj-$(CONFIG_PWM_STI) += pwm-sti.o
> > obj-$(CONFIG_PWM_STM32) += pwm-stm32.o
> > obj-$(CONFIG_PWM_STM32_LP) += pwm-stm32-lp.o
> > diff --git a/drivers/pwm/pwm-sprd.c b/drivers/pwm/pwm-sprd.c
> > new file mode 100644
> > index 0000000..f6fc793
> > --- /dev/null
> > +++ b/drivers/pwm/pwm-sprd.c
> > @@ -0,0 +1,311 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Copyright (C) 2019 Spreadtrum Communications Inc.
>
> If there is a publicly available reference manual available, please add
> a link to it here.
Sure.
>
> > + */
> > +
> > +#include <linux/clk.h>
> > +#include <linux/err.h>
> > +#include <linux/io.h>
> > +#include <linux/math64.h>
> > +#include <linux/module.h>
> > +#include <linux/platform_device.h>
> > +#include <linux/pwm.h>
> > +
> > +#define SPRD_PWM_PRESCALE 0x0
> > +#define SPRD_PWM_MOD 0x4
> > +#define SPRD_PWM_DUTY 0x8
> > +#define SPRD_PWM_DIV 0xc
> > +#define SPRD_PWM_PAT_LOW 0x10
> > +#define SPRD_PWM_PAT_HIGH 0x14
> > +#define SPRD_PWM_ENABLE 0x18
> > +
> > +#define SPRD_PWM_MOD_MAX GENMASK(7, 0)
> > +#define SPRD_PWM_REG_MSK GENMASK(15, 0)
> > +#define SPRD_PWM_ENABLE_BIT BIT(0)
> > +
> > +#define SPRD_PWM_NUM 4
> > +#define SPRD_PWM_REGS_SHIFT 5
> > +#define SPRD_PWM_NUM_CLKS 2
> > +#define SPRD_PWM_DEFAULT_CLK 26000000UL
> > +
> > +struct sprd_pwm_chn {
> > + struct clk_bulk_data clks[SPRD_PWM_NUM_CLKS];
> > + unsigned long clk_rate;
> > + bool clk_enabled;
> > +};
> > +
> > +struct sprd_pwm_chip {
> > + void __iomem *base;
> > + struct device *dev;
> > + struct pwm_chip chip;
> > + int num_pwms;
> > + struct sprd_pwm_chn chn[SPRD_PWM_NUM];
> > +};
> > +
> > +/* list of clocks required by PWM channels */
> > +static const char * const sprd_pwm_clks[] = {
> > + "enable0", "pwm0",
> > + "enable1", "pwm1",
> > + "enable2", "pwm2",
> > + "enable3", "pwm3",
> > +};
> > +
> > +static u32 sprd_pwm_read(struct sprd_pwm_chip *chip, u32 num, u32 reg)
>
> num is the channel id here? Then maybe "hwid" or "chanid" would be a
> better name. Or pass struct pwm_chip only?
Yes, will change to 'hwid'.
>
> Please (if you keep sprd_pwm_chip) rename chip to spc which is the name
> used in other places for structures of this type. "chip" is for struct
> pwm_chip.
Yes, sure.
>
> > +{
> > + u32 offset = reg + (num << SPRD_PWM_REGS_SHIFT);
> > +
> > + return readl_relaxed(chip->base + offset);
> > +}
> > +
> > +static void sprd_pwm_write(struct sprd_pwm_chip *chip, u32 num,
> > + u32 reg, u32 val)
> > +{
> > + u32 offset = reg + (num << SPRD_PWM_REGS_SHIFT);
> > +
> > + writel_relaxed(val, chip->base + offset);
> > +}
> > +
> > +static int sprd_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
> > + int duty_ns, int period_ns)
>
> Please implement .apply() instead of .config(), .enable() and
> .disable().
OK.
>
> > +{
> > + struct sprd_pwm_chip *spc =
> > + container_of(chip, struct sprd_pwm_chip, chip);
> > + struct sprd_pwm_chn *chn = &spc->chn[pwm->hwpwm];
> > + u64 div, tmp;
> > + u32 prescale, duty;
> > + int ret;
> > +
> > + /*
> > + * NOTE: the clocks to PWM channel has to be enabled first before
> > + * writing to the registers.
> > + */
> > + if (!chn->clk_enabled) {
> > + ret = clk_bulk_prepare_enable(SPRD_PWM_NUM_CLKS, chn->clks);
>
> Do you really need to enable all 8 clocks to configure a single channel?
We have 4 channels, and each channel use 2 clocks, so here only enable
2 clocks, see SPRD_PWM_NUM_CLKS.
>
> > + if (ret) {
> > + dev_err(spc->dev, "failed to enable pwm%u clock\n",
> > + pwm->hwpwm);
> > + return ret;
> > + }
> > +
> > + chn->clk_enabled = true;
> > + }
> > +
> > + duty = duty_ns * SPRD_PWM_MOD_MAX / period_ns;
>
> @Baolin: until we're there that there are framework requirements how to
> round, please document at least how you do it here. Also describing the
> underlying concepts would be good for the driver reader.
>
> Something like:
>
> /*
> * The hardware provides a counter that is feed by the source clock.
> * The period length is (PRESCALE + 1) * MOD counter steps.
> * The duty cycle length is (PRESCALE + 1) * DUTY counter steps.
> *
> * To keep the maths simple we're always using MOD = MOD_MAX.
> * The value for PRESCALE is selected such that the resulting period
> * gets the maximal length not bigger than the requested one with the
> * given settings (MOD = MOD_MAX and input clock).
> */
Yes, totally agree with you. I will add some documentation for our
controller's setting.
>
> @Thierry: having a framework guideline here would be good. Or still
> better a guideline and a debug setting that notices drivers stepping out
> of line.
>
> I assume using MOD = 0 is forbidden?
>
> > + /*
> > + * According to the datasheet, the period_ns calculation formula
> > + * should be:
> > + * period_ns = 10^9 * (prescale + 1) * mod / clk_rate
> > + *
> > + * Then we can get the prescale formula:
> > + * prescale = (period_ns * clk_rate) / (10^9 * mod) -1
> > + */
> > + tmp = chn->clk_rate * period_ns;
> > + div = 1000000000ULL * SPRD_PWM_MOD_MAX;
>
> Please use NSEC_PER_SEC instead of 1000000000ULL.
Sure.
>
> > + prescale = div64_u64(tmp, div) - 1;
>
> If tmp is smaller than div you end up with prescale = 0xffffffff which
> should be catched. What if prescale > 0xffff?
Usually we can not meet this case, but you are right, the prescale has
a limit according to the register definition. So will add a validation
here.
>
> > + sprd_pwm_write(spc, pwm->hwpwm, SPRD_PWM_MOD, SPRD_PWM_MOD_MAX);
> > + sprd_pwm_write(spc, pwm->hwpwm, SPRD_PWM_DUTY, duty);
>
> You're losing precision here as you always use SPRD_PWM_MOD_MAX, right?
> (Just for my understanding, if this simpler approach is good enough
> here that's fine.)
Yes, SPRD_PWM_MOD_MAX is good enough.
>
> > + sprd_pwm_write(spc, pwm->hwpwm, SPRD_PWM_PAT_LOW, SPRD_PWM_REG_MSK);
> > + sprd_pwm_write(spc, pwm->hwpwm, SPRD_PWM_PAT_HIGH, SPRD_PWM_REG_MSK);
>
> Please describe these two registers in a short comment.
Sure.
>
> > + sprd_pwm_write(spc, pwm->hwpwm, SPRD_PWM_PRESCALE, prescale);
>
> Is the configuration here atomic in the sense that the write of DUTY
> above only gets effective when PRESCALE is written? If not, please add
Yes.
> a describing paragraph at the top of the driver similar to what is
> written in pwm-sifive.c. When the PWM is already running before, how
> does a configuration change effects the output? Is the currently running
> period completed?
Anyway, I'll add some comments to explain how it works.
>
> > +static void sprd_pwm_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
> > + struct pwm_state *state)
> > +{
> > + struct sprd_pwm_chip *spc =
> > + container_of(chip, struct sprd_pwm_chip, chip);
> > + struct sprd_pwm_chn *chn = &spc->chn[pwm->hwpwm];
> > + u32 enabled, duty, prescale;
> > + u64 tmp;
> > + int ret;
> > +
> > + ret = clk_bulk_prepare_enable(SPRD_PWM_NUM_CLKS, chn->clks);
> > + if (ret) {
> > + dev_err(spc->dev, "failed to enable pwm%u clocks\n",
> > + pwm->hwpwm);
> > + return;
> > + }
> > +
> > + chn->clk_enabled = true;
> > +
> > + duty = sprd_pwm_read(spc, pwm->hwpwm, SPRD_PWM_DUTY) & SPRD_PWM_REG_MSK;
> > + prescale = sprd_pwm_read(spc, pwm->hwpwm, SPRD_PWM_PRESCALE) & SPRD_PWM_REG_MSK;
> > + enabled = sprd_pwm_read(spc, pwm->hwpwm, SPRD_PWM_ENABLE) & SPRD_PWM_ENABLE_BIT;
> > +
> > + /*
> > + * According to the datasheet, the period_ns and duty_ns calculation
> > + * formula should be:
> > + * period_ns = 10^9 * (prescale + 1) * mod / clk_rate
> > + * duty_ns = 10^9 * (prescale + 1) * duty / clk_rate
> > + */
> > + tmp = (prescale + 1) * 1000000000ULL * SPRD_PWM_MOD_MAX;
> > + state->period = div64_u64(tmp, chn->clk_rate);
>
> This is not idempotent. If you apply the configuration that is returned
> here this shouldn't result in a reconfiguration.
Since we may configure the PWM in bootloader, so in kernel part we
should get current PWM state to avoid reconfiguration if state
configuration are same.
>
> > + tmp = (prescale + 1) * 1000000000ULL * duty;
> > + state->duty_cycle = div64_u64(tmp, chn->clk_rate);
> > +
> > + state->enabled = !!enabled;
> > +
> > + /* Disable PWM clocks if the PWM channel is not in enable state. */
> > + if (!enabled) {
> > + clk_bulk_disable_unprepare(SPRD_PWM_NUM_CLKS, chn->clks);
> > + chn->clk_enabled = false;
> > + }
> > +}
> > +
> > +static const struct pwm_ops sprd_pwm_ops = {
> > + .config = sprd_pwm_config,
> > + .enable = sprd_pwm_enable,
> > + .disable = sprd_pwm_disable,
> > + .get_state = sprd_pwm_get_state,
> > + .owner = THIS_MODULE,
> > +};
> > +
> > +static int sprd_pwm_clk_init(struct sprd_pwm_chip *spc)
> > +{
> > + struct clk *clk_parent, *clk_pwm;
> > + int ret, i, clk_index = 0;
> > +
> > + clk_parent = devm_clk_get(spc->dev, "source");
> > + if (IS_ERR(clk_parent)) {
> > + dev_err(spc->dev, "failed to get source clock\n");
> > + return PTR_ERR(clk_parent);
> > + }
> > +
> > + for (i = 0; i < SPRD_PWM_NUM; i++) {
> > + struct sprd_pwm_chn *chn = &spc->chn[i];
> > + int j;
> > +
> > + for (j = 0; j < SPRD_PWM_NUM_CLKS; ++j)
> > + chn->clks[j].id = sprd_pwm_clks[clk_index++];
> > +
> > + ret = devm_clk_bulk_get(spc->dev, SPRD_PWM_NUM_CLKS, chn->clks);
> > + if (ret) {
> > + if (ret == -ENOENT)
> > + break;
>
> devm_clk_bulk_get_optional ? I'm sure you don't want to get all 8 clocks
> 8 times.
This is not optional, each channel has 2 required clocks, and we have
4 channels. (SPRD_PWM_NUM_CLKS == 2)
>
> > +
> > + dev_err(spc->dev, "failed to get channel clocks\n");
> > + return ret;
> > + }
> > +
> > + clk_pwm = chn->clks[1].clk;
>
> This 1 looks suspicious. Are you using all clocks provided in the dtb at
> all? You're not using i in the loop at all, this doesn't look right.
Like I said above, each channel has 2 clocks: enable clock and pwm
clock, the 2nd clock of each channel's bulk clocks is the pwm clock,
which is used to set the source clock. I know this's not easy to read,
so do you have any good suggestion?
>
> > + if (!clk_set_parent(clk_pwm, clk_parent))
> > + chn->clk_rate = clk_get_rate(clk_pwm);
> > + else
> > + chn->clk_rate = SPRD_PWM_DEFAULT_CLK;
>
> I don't know all the clock framework details, but I think there are
> better ways to ensure that a given clock is used as parent for another
> given clock. Please read the chapter about "Assigned clock parents and
> rates" in the clock bindings and check if this could be used for the
> purpose here and so simplify the driver.
Actually there are many other drivers set the parent clock like this,
and we want a default clock if failed to set the parent clock.
>
> > + }
> > +
> > + if (!i) {
> > + dev_err(spc->dev, "no availbale PWM channels\n");
>
> s/availbale/available/
Sure.
>
> > + return -EINVAL;
> > + }
> > +
> > + spc->num_pwms = i;
> > +
> > + return 0;
> > +}
> > +
> > +static int sprd_pwm_probe(struct platform_device *pdev)
> > +{
> > + struct sprd_pwm_chip *spc;
> > + int ret;
> > +
> > + spc = devm_kzalloc(&pdev->dev, sizeof(*spc), GFP_KERNEL);
> > + if (!spc)
> > + return -ENOMEM;
> > +
> > + spc->base = devm_platform_ioremap_resource(pdev, 0);
> > + if (IS_ERR(spc->base))
> > + return PTR_ERR(spc->base);
> > +
> > + spc->dev = &pdev->dev;
> > + ret = sprd_pwm_clk_init(spc);
> > + if (ret)
> > + return ret;
> > +
> > + spc->chip.dev = &pdev->dev;
> > + spc->chip.ops = &sprd_pwm_ops;
> > + spc->chip.base = -1;
> > + spc->chip.npwm = spc->num_pwms;
> > +
> > + ret = pwmchip_add(&spc->chip);
> > + if (ret) {
> > + dev_err(&pdev->dev, "failed to add PWM chip\n");
> > + return ret;
> > + }
> > +
> > + platform_set_drvdata(pdev, spc);
>
> If you do this earlier you can simplify the last part of the driver to:
>
> ret = pwmchip_add(&spc->chip);
> if (ret)
> dev_err(&pdev->dev, "failed to add PWM chip\n");
>
> return ret;
OK.
>
> > + return 0;
> > +}
> > +
> > +static int sprd_pwm_remove(struct platform_device *pdev)
> > +{
> > + struct sprd_pwm_chip *spc = platform_get_drvdata(pdev);
> > + int i;
> > +
> > + for (i = 0; i < spc->num_pwms; i++)
> > + pwm_disable(&spc->chip.pwms[i]);
>
> This is wrong. You must not call pwm_disable here. It's the consumer's
> responsibility to disable the hardware.
Emm, I saw some drivers did like this, like pwm-spear.c.
Could you elaborate on what's the problem if the driver issues pwm_disable?
Very appreciated for your comments.
--
Baolin Wang
Best Regards
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